In 32-bit system the unix timestamp will overflow if the date goes beyond year 2038 and this method will return false. In 64-bit systems this function will still work as intended. For more information please see http://en.wikipedia.org/wiki/Year_2038_problem.

Note that getTimestamp() does not return the UTC timestamp. It returns the timestamp relative to the set timezone, or the default server timezone. This also applies to dates in timezones with Daylight Savings.